1. Field of the Invention
The present invention relates to an apparatus used to fasten ceramic matrix composites (CMCs) to metallic components.
2. Description of Related Art
Conventional gas turbine engines operate at harsh environmental conditions characterized by high temperatures, high pressures and intense mechanical and acoustic vibrations. Engine manufacturers are in search of new advanced materials that are capable of providing improved durability, greater thrust, longer life, and superior overall performance to replace current state of the art nickel based superalloys. Those skilled in the art of manufacturing engines have identified ceramic matrix composites (CMCs) as having qualities that far surpass the performance capabilities of nickel based superalloys. CMCs can withstand higher temperature conditions, have greater weight reduction capabilities and improved durability over other state of the art materials. CMCs have especially good vibrational damping capabilities and a low coefficient of thermal expansion.
While CMCs do have many advantages, they also present design challenges, especially in their application to hot section engine components. These limitations make it difficult to design fastening systems to attach CMCs to metallic engine components. Most traditional CMCs fastening systems are unable to withstand or dissipate heavy loads and their design often leads to space constraints on the rest of the engine system. One such fastening system uses a combination of screw and rivet technology. This fastening method unavoidably leaves machined holes in the CMC. These holes can result in stress concentrations and increase the likelihood of CMC fracture.
Another method of fastening CMCs to metallic engine components is a CMC self-sealing approach where oxygen entering the engine is consumed in the CMC microcracks. This method prevents access to the carbon matrix interface creating a sealcoat but the sealcoat is prone to degradation. This fastening system does have a high degree of damage tolerance however, it is not enough to sustain the heavy loads and high temperatures that exist during engine assembly.
Accordingly, there is a need for a fastening apparatus that can overcome, alleviate, and/or mitigate one or more of the aforementioned and other deleterious effects of prior art. A novel apparatus is needed that will reduce space constraints, dampen mechanical and acoustic vibrations, compensate for the mismatch in thermal expansion between CMC and metal, and be able to sustain and/or dissipate extreme acoustic, thermal and weight bearing loads that are often not withstandable using traditional apparatuses.